Abstract
AbstractThe cold‐dense plasma sheet (CDPS) plays an important role in the entry process of the solar wind plasma into the magnetosphere. Investigating the seasonal variation of CDPS occurrences will help us better understand the long‐term variation of plasma exchange between the solar wind and magnetosphere, but any seasonal variation of CDPS occurrences has not yet been reported in the literature. In this paper, we investigate the seasonal variation of the occurrence rate of CDPS using Geotail data from 1996 to 2015 and find a semiannual variation of the CDPS occurrences. Given the higher probability of solar wind entry under stronger northward interplanetary magnetic field (IMF) conditions, 20 years of IMF data (1996–2015) are used to investigate the seasonal variation of IMF Bz under northward IMF conditions. We find a semiannual variation of IMF Bz, which is consistent with the Russell‐McPherron (R‐M) effect. We therefore suggest that the semiannual variation of CDPS may be related to the R‐M effect.
Highlights
The formation of the cold-dense plasma sheet (CDPS) is considered a representative signature of solar wind entry under northward interplanetary magnetic field (IMF) conditions seen in the magnetosphere (e.g., Fujimoto et al, 1996; Stenuit et al, 2002; Terasawa et al, 1997; Wing & Newell, 2002)
We found that most of the CDPS events in our study are during quiet times (Kp < 3 and AE < 150 nT; see Figure S2); the semiannual variation of CDPS occurrence should not be related to solar wind entry under southward IMF conditions prior to the identified events
We have performed a statistical analysis of the occurrence of the CDPS and the magnitude of the northward IMF Bz
Summary
The formation of the cold-dense plasma sheet (CDPS) is considered a representative signature of solar wind entry under northward interplanetary magnetic field (IMF) conditions seen in the magnetosphere (e.g., Fujimoto et al, 1996; Stenuit et al, 2002; Terasawa et al, 1997; Wing & Newell, 2002). The equinoctial hypothesis considers the φ angle between the Earth-Sun line and the dipole axis of the Earth as the key parameter that affects the field configuration in the Chapman-Ferraro current plane (Crooker & Siscoe, 1986) This suppresses the transfer of energy and further influences the coupling efficiency between solar wind and magnetosphere. In this paper, we investigate the seasonal variation of CDPS occurrences and the possible role that the R-M effect plays in the seasonal variation of northward IMF, and build a possible link between the R-M effect and the CDPS occurrences
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